U.S. patent number 5,207,159 [Application Number 07/879,841] was granted by the patent office on 1993-05-04 for coating apparatus for sheet-fed, offset rotary printing presses.
This patent grant is currently assigned to Howard W. DeMoore. Invention is credited to Howard W. DeMoore, Steven M. Person.
United States Patent |
5,207,159 |
DeMoore , et al. |
May 4, 1993 |
**Please see images for:
( Certificate of Correction ) ** |
Coating apparatus for sheet-fed, offset rotary printing presses
Abstract
A coating apparatus for use in a sheet-fed or web-fed, offset
rotary or flexographic printing press to apply a protective and/or
decorative coating to the surface or freshly printed sheets
includes a doctor blade coating unit coupled to a pickup roller for
supplying liquid material from a reservoir to the surface of a
pickup roller mounted on a press delivery drive shaft. Liquid
material is circulated through the reservoir of the doctor blade
unit by suction flow produced by a return pump. This prevents the
buildup of a positive pressure differential within the doctor blade
reservoir. The doctor blade reservoir is maintained at below
ambient pressure level, thereby preventing leakage through the end
seals. A vacuum sensor circuit provides a visual indication of air
vacuum pressure in the doctor blade reservoir chamber, and a vacuum
sensor switch applies electrical power to an audio transducer. The
audio transducer produces an audible alarm in response to an
increase in doctor blade chamber pressure, thereby providing
advance warning of an impending end seal failure or a worn doctor
blade condition.
Inventors: |
DeMoore; Howard W. (Dallas,
TX), Person; Steven M. (Seagoville, TX) |
Assignee: |
DeMoore; Howard W. (Plano,
TX)
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Family
ID: |
25374982 |
Appl.
No.: |
07/879,841 |
Filed: |
May 6, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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752778 |
Aug 30, 1991 |
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Current U.S.
Class: |
101/350.1;
118/262; 101/367; 101/148; 118/261; 101/351.1 |
Current CPC
Class: |
B05C
1/086 (20130101); B41F 30/04 (20130101); B41F
13/0008 (20130101); B05C 1/0813 (20130101); B41F
23/08 (20130101); B41F 31/027 (20130101); B41F
31/36 (20130101); B41P 2200/12 (20130101) |
Current International
Class: |
B05C
1/08 (20060101); B41F 13/00 (20060101); B41F
31/36 (20060101); B41F 23/08 (20060101); B41F
30/00 (20060101); B41F 30/04 (20060101); B41F
23/00 (20060101); B41F 31/02 (20060101); B41F
31/00 (20060101); B41F 031/00 () |
Field of
Search: |
;101/135,147,148,157,167,169,207,208,210,329,330,331,348,349,350,351,364,365,366
;118/602,612,236,242,259,261 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Eickholt; Eugene H.
Attorney, Agent or Firm: Griggs; Dennis T.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of application Ser. No.
07/752,778 filed Aug. 30, 1991.
Claims
What is claimed is:
1. Apparatus for applying liquid material from a supply to a pickup
roller comprising in combination:
a doctor blade head having an elongated reservoir for receiving
liquid material from the supply, said doctor blade head being
adapted to extend in parallel with the pickup roller in an
operative position with a portion of the peripheral surface of the
pickup roller extending into said reservoir for wetting contact
with liquid material contained therein, and two doctor blades
attached to said doctor blade head for engagement against said
peripheral surface in the operative position;
a supply conduit connecting said supply in flow communication with
said reservoir;
a return conduit connecting said reservoir in flow communication
with said supply; and,
a first pump coupled in series flow relation with said return
conduit for inducing suction flow of liquid material from said
reservoir through said return conduit into said supply.
2. Apparatus as defined in claim 1, including:
a second pump coupled in series flow relation with said supply
conduit for pumping liquid material from said supply to said
reservoir.
3. Apparatus as defined in claim 2, wherein the suction return
pumping rate of said first pump is greater than the supply pumping
rate of said second pump.
4. Apparatus as defined in claim 1, said doctor blade head having
first and second shoulders forming lower and upper liquid level
boundaries for said reservoir, respectively, wherein the return
conduit is coupled in flow communication with said reservoir at a
liquid level location disposed intermediate the liquid level
boundaries established by said first and second shoulders.
5. Apparatus as defined in claim 1, wherein the return conduit is
coupled in flow communication with said reservoir at a first liquid
level location and the supply conduit is coupled in flow
communication with said reservoir at a second liquid level
location, the first liquid level location of the return conduit
being higher in elevation than the second liquid level location of
the supply conduit when the doctor blade head is in the operative
position.
6. Apparatus for applying liquid material from a supply to a pickup
roller comprising, in combination:
an elongated doctor blade head having an elongated cavity formed
therein defining a reservoir for receiving liquid material from the
supply, said doctor blade head being adapted to extend in parallel
with the pickup roller in an operative position with a portion of
the peripheral surface of the pickup roller extending into said
cavity for wetting contact with liquid material contained therein,
and a pair of doctor blades disposed on opposite sides of said
cavity and extending the length thereof for engagement against the
peripheral surface of the pickup roller in the operative position;
and,
means coupled to said supply and to said reservoir for inducing
flow of liquid material from said supply into said reservoir and
for returning excess liquid material by suction force from said
reservoir to said supply.
7. Apparatus as defined in claim 6, said inducing means
comprising:
a supply conduit connecting said supply in flow communication with
said reservoir;
a return conduit connecting said reservoir in flow communication
with said supply; and,
a first pump coupled in series flow relation with said return
conduit for inducing suction flow of liquid material from said
supply through said supply conduit into said reservoir, and for
inducing suction flow of liquid material from said reservoir
through said return conduit into said supply.
8. Apparatus as defined in claim 7, said means including:
a second pump coupled in series flow relation with said supply
conduit for pumping liquid material from said supply to said
reservoir.
9. Apparatus as defined in claim 8, wherein the suction return
pumping rate of said first pump is greater than the supply pumping
rate of said second pump.
10. Apparatus as defined in claim 6, said doctor blade head having
first and second shoulders forming lower and upper liquid level
boundaries for said reservoir, respectively, wherein said means for
inducing suction flow includes a return conduit coupled in flow
communication with said reservoir at a liquid level location
disposed intermediate the liquid level boundaries established by
said first and second shoulders.
11. Apparatus for applying liquid material from a supply to a
pickup roller comprising in combination:
a doctor blade head having an elongated reservoir for receiving
liquid material from the supply, said doctor blade head being
adapted to extend in parallel with the pickup roller in an
operative position with a portion of the peripheral surface of the
pickup roller extending into said reservoir for wetting contact
with liquid material contained therein, and two doctor blades
attached to said doctor blade head for engagement against said
peripheral surface in the operative position;
first means coupled to said supply and to said reservoir for
pumping liquid material from said supply into said reservoir;
and,
second means coupled to said reservoir and to said supply for
inducing suction flow of liquid material from said reservoir into
said supply.
12. Apparatus for applying liquid material from a supply to a
pickup roller comprising in combination:
a doctor blade head having an elongated reservoir chamber for
receiving liquid material from the supply, said doctor blade head
being adapted to extend in parallel with the pickup roller in an
operative position with a portion of the peripheral surface of the
pickup roller extending into said reservoir chamber for wetting
contact with liquid material contained therein, and two doctor
blades attached to said doctor blade head for engagement against
said peripheral surface in the operative position; and,
a suction pump coupled to said reservoir and to said supply for
inducing suction flow of liquid material from said reservoir to
said supply.
13. Apparatus as defined in claim 12, including a pneumatic sensor
conduit coupled to said reservoir chamber for sensing the air
vacuum pressure within said reservoir chamber, and a vacuum gauge
coupled to said sensor conduit for providing a visual indication of
air vacuum pressure in said reservoir chamber.
14. Apparatus as defined in claim 12, including a pneumatic sensor
conduit coupled to said reservoir chamber for sensing the air
vacuum pressure within said reservoir chamber, a vacuum responsive
switch having a sensing chamber coupled to said sensor conduit and
switch electrodes and an audio transducer electrically connected to
said switch electrodes for making and breaking an electrical
circuit from a power source to said audio transducer.
15. In a sheet-fed, offset rotary printing press of the type
including at least one printing station having a blanket cylinder
and an impression cylinder disposed for printing ink onto sheets
passing therebetween, and a delivery conveyor system for pulling
freshly printed sheets from the impression cylinder and
transporting the printed sheets toward a sheet delivery stacker,
the delivery conveyor system including a delivery drive shaft
disposed adjacent to and extending parallel with the impression
cylinder and driven in timed synchronous relation with the
impression cylinder, the improvement comprising:
a delivery cylinder mounted onto said delivery drive shaft and
having an outer peripheral support surface adapted to engage and
support a sheet being transported by said delivery conveyor
system;
a coating apparatus including a supply of liquid material, a
rotatable pickup roller having an outer peripheral surface of
substantially cylindrical shape, and means for applying a coating
of liquid material from said supply onto said outer peripheral
surface of said pickup roller;
means for mounting said coating apparatus to the press adjacent
said delivery cylinder with a portion of said peripheral surface of
said pickup roller engaged with the support surface of said
delivery cylinder, whereby liquid coating material from said supply
applied onto the peripheral surface of said pickup roller is
transferred to said support surface of said delivery cylinder and
to said freshly printed sheet;
said coating apparatus including an elongated reservoir for
receiving liquid material from said supply, said reservoir
extending parallel with said pickup roller with a portion of the
peripheral surface of the pickup roller extending into said
reservoir for wetting contact with liquid material contained
therein, and two doctor blades attached to said reservoir and
engaging said peripheral surface, said doctor blades acting to
limit the amount of liquid material applied onto said peripheral
surface from said reservoir;
a supply conduit connecting said supply in flow communication with
said reservoir;
a return conduit connecting said reservoir in flow communication
with said supply; and,
a first pump coupled in series flow relation with said return
conduit for inducing suction flow return of liquid material from
said reservoir to the remote supply.
16. The improvement as set forth in claim 15, wherein said coating
apparatus is mounted to said press downstream of said delivery
drive shaft in the direction of travel of said sheets during
transport by said delivery conveyor system.
17. The improvement as set forth in claim 15, including:
a second pump coupled in series flow relation with said supply
conduit for liquid material from the remote supply to said
reservoir.
18. The improvement as set forth in claim 17, wherein the suction
return flow rate of said first pump is greater than the positive
pressure supply flow rate of said second pump.
19. The improvement as set forth in claim 15, wherein the return
conduit is coupled in flow communication with said reservoir at a
first liquid level location and the supply conduit is coupled in
flow communication with said reservoir at a second liquid level
location, the first liquid level location of the return conduit
being higher than the second liquid level location of the supply
conduit.
20. In a sheet-fed, offset rotary printing press of the type
including at least one printing station having a blanket cylinder
and an impression cylinder disposed for printing wet ink onto
sheets passing therebetween, and a delivery conveyor system for
pulling freshly printed sheets from the impression cylinder and
transporting the printed sheets toward a sheet delivery stacker,
the delivery conveyor system comprising a pair of endless gripper
chains disposed on opposite sides of the press and supporting
therebetween gripper bars and grippers spaced along the chains, the
gripper chains being driven in timed synchronous relation with the
impression cylinder by laterally spaced sprocket wheels mounted on
opposite ends of a delivery drive shaft disposed adjacent to and
extending parallel with the impression cylinder, the improvement
comprising:
a delivery cylinder mounted to said delivery drive shaft between
said sprocket wheels and having an outer peripheral support surface
covered by a removable coating blanket adapted to engage and
support the wet ink side of a sheet being transported by said
gripper bars;
a coating apparatus including a supply of liquid material, a
rotatable pickup roller having an outer peripheral surface of
substantially cylindrical shape, and means for applying liquid
material from said supply onto said peripheral surface of said
pickup roller;
means for mounting said coating apparatus to the press adjacent the
delivery cylinder, with a portion of the outer peripheral surface
of said pickup roller engaged with said delivery cylinder, whereby
liquid material doctored onto the peripheral surface of said pickup
roller is transferred to said delivery cylinder and to said freshly
printed sheet;
said coating apparatus including an elongated reservoir containing
liquid material, said reservoir being disposed to extend parallel
with said pickup roller with a portion of said peripheral surface
extending into said reservoir in contact with liquid material
contained therein, and two doctor blades attached to said reservoir
and engaging said peripheral surface, said doctor blades acting to
limit the amount of liquid coating material applied onto said
peripheral surface from said reservoir;
a supply conduit connecting said supply in flow communication with
said reservoir;
a return conduit connecting said reservoir in flow communication
with said supply; and,
a first pump coupled in series flow relation with said return
conduit for inducing suction flow return of liquid material from
said reservoir to said supply.
21. A sheet-fed, offset rotary printing press including:
at least one printing station having a blanket cylinder and an
impression cylinder disposed for printing wet ink onto sheets
passing therebetween;
a delivery conveyor system for pulling freshly printed sheets from
the impression cylinder and transporting the printed sheets toward
a sheet delivery stacker, the delivery system including a delivery
drive shaft;
a delivery cylinder mounted to said delivery drive shaft and having
an outer peripheral support surface adapted to engage and support a
sheet being transported by said delivery conveyor system;
a coating apparatus including a supply of liquid material, a
rotatable pickup roller having an outer peripheral surface of
substantially cylindrical shape, and means for applying liquid
material from said supply onto the peripheral surface of said
pickup roller;
means for mounting said coating apparatus to the press adjacent
said delivery cylinder, with a portion of said peripheral surface
of said pickup roller engaged with said delivery cylinder, whereby
liquid material applied to the peripheral surface of said pickup
roller is transferred to said delivery cylinder and then to said
freshly printed sheet;
said coating apparatus including an elongated reservoir containing
liquid material, said reservoir being disposed to extend parallel
with said pickup roller with a portion of said peripheral surface
extending into the reservoir in contact with liquid material
contained therein, and two doctor blades attached to said reservoir
and engaging said peripheral surface, said doctor blades acting to
limit the amount of liquid coating material applied onto said
peripheral surface from said reservoir;
a supply conduit connecting said supply in flow communication with
said reservoir;
a return conduit connecting said reservoir in flow communication
with said supply; and,
a first pump coupled in series flow relation with said return
conduit for inducing suction flow return of liquid material from
said reservoir to said supply.
Description
FIELD OF THE INVENTION
This invention relates to sheet-fed or web-fed, offset rotary or
flexographic printing presses, and more particularly, to a new and
improved apparatus for the in-line application of protective and
decorative coatings or inks to the printed surface of freshly
printed sheets or web.
BACKGROUND OF THE INVENTION
Conventional sheet-fed, offset rotary printing presses typically
include one or more printing stations through which individual
sheets are fed and printed with wet ink. After final printing, the
sheets are fed by a delivery conveyor system to the delivery end of
the press where the freshly printed sheets are collected and
stacked. In a typical sheet-fed, offset rotary printing press such
as the Heidelberg Speedmaster line of presses, the delivery
conveyor system includes a pair of endless gripper chains carrying
spaced laterally disposed gripper bars and grippers which are used
to grip and pull freshly printed sheets from the impression
cylinder and convey the sheets toward the sheet delivery stacker.
The gripper chains are driven in precisely timed relation to the
impression cylinder by gripper chain sprocket wheels which are
laterally spaced between a delivery drive shaft mounted on opposite
sides of the press frame. The delivery drive shaft is mechanically
coupled by gears for synchronous rotation with the impression
cylinder.
Since the inks used with offset type printing presses typically
remain wet and tacky for some time after printing, special
precautions must be taken to insure that the wet inked surface of
the freshly printed sheets is not marked or smeared as the sheets
are transferred from one printing station to another, and through
the delivery system to the sheet delivery stacker. The printed
surface of the paper dries relatively slowly and can be smeared
during subsequent processing, particularly when the printed sheets
are stacked. In order to minimize smearing, a dryer may be mounted
along the delivery path of the printed sheets, or an anti-offset
spray powder may be sprayed on the printed surface.
In some printing applications, it is desirable that the press be
capable of applying a protective and/or decorative coating over all
or a portion of the surface of the printed sheets. Typical coating
solutions include varnish, lacquer, dye, moisturizers and ink. Such
coatings typically are formed of a UV-curable or water-soluble
resin applied as a liquid solution or emulsion by an applicator
roller over the freshly printed sheets to protect the ink and
improve the appearance of the sheets. Use of such coatings is
particularly desirable when decorative or protective finishes are
required such as in the production of posters, record jackets,
brochures, magazines, folding cartons and the like. In cases where
a liquid coating is to be applied, the coating operation is carried
out after the final ink printing has been performed, most desirably
by an in-line coating application.
DESCRIPTION OF THE PRIOR ART
Various suggestions have been made for applying the coating as an
in-line press operation by using the final printing station of the
press as the coating application station. For example, in U.S. Pat.
Nos. 4,270,483, 4,685,414 and 4,779,557, there are disclosed
coating apparatus which can be moved into position to allow the
blanket cylinder of the last printing station of a press to be used
to apply a coating material to the sheets. In U.S. Pat. No.
4,796,556, there is disclosed a coating apparatus which can be
selectively moved between the blanket cylinder or the plate
cylinder of the last printing station of the press so that the
station can be used as a coating station for the press.
Suggestions for overcoming the problem of the loss of a printing
station when coating is desired have also been made, such as that
set forth in U.S. Pat Nos. 4,934,305 which discloses a coating
apparatus having a separate timed applicator roller positioned to
apply the coating material to the printed sheet while the sheet is
on the last impression cylinder of the press. This is said to allow
the last printing station to be operated simultaneously as both an
ink application station and a coating station so that no loss of
press printing unit capability results. Another approach to
providing a coating station without losing the printing
capabilities of the last printing station is to provide a totally
separate coating unit downstream of the last printing station so
that the coating is applied to the sheets after final printing and
before the sheets have reached the sheet delivery stacker. Such an
approach is suggested in U.S. Pat. Nos. 4,399,767 and
4,706,601.
Conventional coating apparatus which is operable as an in-line
press operation utilizes an engraved transfer roller, with the
liquid coating being applied to the engraved roller by means of a
doctor blade assembly. The doctor blade assembly includes an
elongated housing having a reservoir chamber extending the length
of the transfer roller for holding a volume of coating liquid in
wetting contact with the circumferential surface of the transfer
roller. A pair of circumferentially spaced doctor blades extend
longitudinally along the reservoir housing on either side of the
chamber. The doctor blades are angled tangentially toward the
transfer roller surface, and seal the reservoir chamber against the
roller surface and wipe the roller surface to deposit liquid in the
cells of the engraved transfer surface.
The reservoir chamber is pressurized with coating liquid, which is
pumped from a remote supply drum into the upper region of the
pressure chamber. After the pressure chamber fills to a certain
level, it is returned to the remote drum by gravity flow.
Occasionally, the doctor blade reservoir chamber becomes completely
filled with the coating liquid when the volume of coating liquid
being delivered to the doctor blade reservoir chamber exceeds the
gravity flow return rate. The positive pressure may cause the seals
at the ends of the roller to leak, allowing the coating liquid to
drip onto the floor or onto adjacent press parts. Occasionally, the
coating liquid may be slung from the roller onto adjacent press
equipment and operator areas. Moreover, the buildup of positive
pressure within the doctor blade reservoir chamber accelerates the
wear of the end seals.
It will be appreciated that the transfer roller may be operated at
high speeds, for example, on the order of 1,000 linear feet per
minute, and that the end seals of the doctor blade assembly will
tend to wear quickly. The end seal wear is accelerated by the
buildup of positive pressure within the doctor blade chamber. Low
volume drip leakage can be collected in a drip pan or catch tray,
but as the end seals wear, the coating liquid will be slung from
the transfer roller, thereby causing a difficult cleanup problem.
When this occurs, the press must be shut down, the doctor blade
head must be removed, and the end seals replaced. The steps of
rebuilding or replacing the end seals and realigning the doctor
blade head causes an unacceptable amount of press downtime.
One approach for overcoming the problem of end seal wear is to
provide stationary end seals which are mounted on the press frame,
and which bear in sealing engagement against the ends of the
transfer roller, so that the doctor blade head may form a seal with
stationary seals rather than with the dynamic seals carried on the
transfer roller. Another approach is to use rotary end seals which
include an end plate which is resiliently engaged against the end
surface of the transfer roller, with a seal member being secured
between the end plate and the end portions of the roller by quick
removal mounting lugs.
While the foregoing mechanical approaches to limiting end seal wear
and thereby avoiding leakage have been moderately successful, and
some arrangements have reduced downtime by quick change mounting
features, the end seals nevertheless are still experiencing
accelerated wear and early failure, thereby causing frequent
replacements and unacceptable downtime for correction of end seal
leakage.
OBJECTS OF THE INVENTION
Accordingly, there exists a need for a new and improved in-line
coating apparatus for use in a sheet-fed or web-fed, offset rotary
or flexographic printing press for applying a protective and/or
decorative coating to the printed surface of freshly printed sheets
which does not require any expensive or substantial press
modification or result in any impairment of normal press operating
capability.
Specifically, the principal object of the present invention is to
provide a new and improved in-line coating and/or inking apparatus
of the character described which achieves a reduction in end seal
leakage.
SUMMARY OF THE INVENTION
The present invention provides a new and improved inline doctor
blade apparatus for applying a protective and/or decorative coating
and/or inking to the surface of freshly printed sheets in a
sheet-fed or web-fed, offset rotary or flexographic printing press
which is highly reliable and effective in use, yet which does not
require any expensive or substantial press modification or result
in any impairment of normal press operating capability.
The reservoir of a doctor blade head is supplied with coating
material from a remote supply drum. To insure that an adequate
supply of coating liquid is always present within the doctor blade
reservoir, the coating material is drawn from the remote supply
drum and is circulated by suction flow constantly through the
reservoir. In contrast to the conventional approach of positively
pressurizing the doctor blade reservoir with liquid coating pumped
from the remote drum to the reservoir, the coating material is
instead circulated through the reservoir by suction flow. That is,
instead of charging the reservoir with coating liquid pumped from
the remote drum and thereby creating a positive pressure condition
within the doctor blade reservoir, circulation through the
reservoir is induced by suction flow provided by a suction pump
having an input connected for drawing coating liquid from the
doctor blade reservoir, and returning it by forced (positive
pressure) flow to the remote supply drum, rather than by gravity
flow return.
As a result of the suction flow arrangement, the liquid material is
drawn from the remote supply drum at a greater rate than the rate
of withdrawal of the liquid material by the pickup roller, and a
substantially constant supply of liquid material will always be
present within the doctor blade reservoir. A benefit of the suction
flow arrangement is that a positive pressure buildup does not occur
within the doctor blade chamber. Moreover, liquid material which
rises above a predetermined fill level is drawn out of the doctor
blade reservoir by the suction pump, and is returned to the remote
drum. Consequently, the end seals are not subjected to high
pressure differential conditions. Instead, the suction flow
arrangement produces a negative pressure differential, with the
doctor blade chamber being operated at a level below atmospheric.
Under negative pressure conditions, leakage of coating liquid is
virtually non-existent, and the operating life of the end seals is
substantially increased.
According to another aspect of the present invention, visual and
audible alerts are provided by a vacuum sensor line which is
coupled to the vacuum space within the doctor blade chamber. The
sensor line is coupled to a vacuum gauge which provides a visual
indication of the suction pressure within the doctor blade chamber.
A vacuum sensor switch is also coupled to the chamber for
selectively applying electrical power to an audio transducer when
the pressure within the vacuum chamber rises above a predetermined
safe operating suction level.
Other features and advantages of the present invention will become
more apparent from the following detailed description taken in
conjunction with the accompanying drawings which disclose, by way
of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevational view of a sheet-fed, offset
rotary printing press having a coating apparatus embodying the
present invention;
FIG. 2 is an enlarged fragmentary side elevational view taken
substantially within the circular area designated "2" in FIG. 1 and
showing the coating apparatus of the present invention during
coating operation;
FIG. 3 is an enlarged fragmentary perspective view showing one side
of the coating apparatus mounted in the press and illustrating the
fluid path of coating material from a remote supply drum to the
doctor blade reservoir of the coating unit;
FIG. 4 is an enlarged fragmentary sectional view taken
substantially along the line 4--4 of FIG. 3;
FIG. 5 is a simplified flow diagram which illustrates a dual pump
arrangement for circulating coating liquid from a remote supply
drum to the doctor blade reservoir and return;
FIG. 6 is a simplified flow diagram which illustrates a single pump
arrangement for circulating coating liquid by suction flow from a
remote supply drum to the doctor blade reservoir and return;
FIG. 7 is an enlarged fragmentary perspective view of one end
portion of the doctor blade coating apparatus of the present
invention;
FIG. 8 is an enlarged sectional view taken substantially along the
line 8--8 of FIG. 7; and,
FIG. 9 is a view similar to FIG. 8 which includes a suction
pressure sensing circuit for providing a visual indication of
suction pressure and an audible alert when the suction/vacuum
pressure inside the doctor blade rises above a safe operating
level, thereby signaling an impending end seal failure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the exemplary drawings, the present invention is
embodied in a new and improved in-line doctor blade apparatus,
herein generally designated 10, for use in applying a protective
and/or decorative coating or inks to the freshly printed surface of
sheets printed in a sheet-fed or web-fed, offset rotary or
flexographic printing press, herein generally designated 12. In
this instance, as shown in FIG. 1, the doctor blade coating
apparatus 10 is illustrated as installed in a four color printing
press 12, such as that manufactured by Heidelberger Druckmaschinen
AG of the Federal Republic of Germany under its designation
Heidelberg Speedmaster 102V (40"), and which includes a press frame
14 coupled at one end, herein the right end, with a sheet feeder 16
from which sheets, herein designated 18, are individually and
sequentially fed into the press, and at the opposite end, with a
sheet delivery stacker 20 in which the finally printed sheets are
collected and stacked. Interposed between the sheet feeder 16 and
the sheet delivery stacker 20 are four substantially identical
sheet printing stations 22, 24, 26 and 28 which can print different
color inks onto the sheets as they are moved through the press
10.
As illustrated, each of the printing stations 22, 24, 26 and 28 is
substantially identical and of conventional design, herein
including a sheet-fed cylinder 30, a plate cylinder 32, a blanker
cylinder 34 and an impression cylinder 36, with each of the first
three printing stations 22, 24 and 26 having a transfer cylinder 38
disposed to withdraw the freshly printed sheets from the adjacent
impression cylinder and transfer the freshly printed sheets to the
next printing station via a transfer drum 40. The final printing
station 28 herein is shown as equipped with a delivery cylinder 42
which functions to support the printed sheet 18 as it is moved from
the final impression cylinder 36 by a delivery conveyor system,
generally designated 44, to the sheet delivery stacker 20.
The delivery conveyor system 44 as shown in FIG. 2 is of
conventional design and includes a pair of endless delivery gripper
chains 46, only one of which is shown carrying at regular spaced
locations along the chains, laterally disposed gripper bars 48
having gripper elements 50 used to grip the leading edge of a sheet
18 after it leaves the nip between the delivery cylinder 42 and
impression cylinder 36 of the last printing station 28. As the
leading edge E of the sheet 18 is gripped by the grippers 50 the
delivery chains 46 pull the sheet away from the impression cylinder
36 and convey the freshly printed sheet to the sheet delivery
stacker 20 where the grippers release the finally printed
sheet.
The endless delivery chains 46 are driven in synchronous timed
relation to the impression cylinder 36 by sprocket wheels 52 fixed
adjacent the lateral ends of a delivery drive shaft 54 which has a
mechanically geared coupling (not shown) to the press drive system.
The delivery drive shaft 54 extends laterally between the sides of
the press frame 14 adjacent the impression cylinder 36 of the last
printing station 28, and is disposed to be parallel with the axis
of the impression cylinder. In this instance, the delivery cylinder
42, which is constructed to allow adjustments in diameter by
suitable means, is attached to the delivery drive shaft 54 so that
the delivery cylinder is also rotated in precise timed relation
with the impression cylinder.
In this respect, it is important to note that when the freshly
printed sheets 18 are conveyed away from the impression cylinder 36
of the final printing station 28 by the gripper 50 carried by the
delivery chains 46, the wet inked surfaces of the sheets face the
delivery drive shaft 54 and the sheets must be supported such that
the ink is not smeared as the sheets are transferred. Typically,
such support is provided by skeleton wheels or cylinders mounted to
the press delivery drive shaft 54, or as is now more commonly used,
net equipped delivery cylinders marketed by Printing Research, Inc.
of Dallas, Tex. under its registered trademark SUPERBLUE. That
system, which is made and sold under license, is manufactured in
accordance with and operates as described in U.S. Pat. No.
4,402,267, issued Sep. 6, 1983, to Howard W. DeMoore, the
disclosure of which is incorporated herein by this reference.
More recently, vacuum transfer apparatus of the type disclosed in
co-pending U.S. application Ser. No. 07/630,308, filed Dec. 18,
1990, entitled "Vacuum Transfer Apparatus for Sheet-Fed Printing
Presses", which is also incorporated herein by reference, has been
used. The vacuum transfer apparatus disclosed in that application
can be used in place of delivery cylinders or skeleton wheels to
pull the unprinted side of the sheet away from the delivery drive
shaft 54 so that the wet ink surface of the sheets do not come into
contact with any press apparatus.
In accordance with the present invention, the in-line doctor blade
coating apparatus 10 for applying the protective or decorative
coating or ink to the sheets 18 enables the press 12 to be operated
in the normal manner without the loss of the final printing station
28, and without requiring any substantial press modifications by
employing the existing press delivery drive shaft 54 as the
mounting location for the coating applicator roller. In presses
having delivery systems such as skeleton wheels mounted on the
delivery drive shaft 54 or a vacuum transfer apparatus as disclosed
in the aforementioned co-pending U.S. application Ser. No.
07/630,308, conversion to a coating operation can be quickly and
easily achieved by mounting on the press delivery drive shaft in
place of the skeleton wheels or in addition to the vacuum transfer
apparatus, a suitable support cylinder capable of performing the
combined function of a coating applicator roller and a net enhanced
delivery cylinder 42. By utilizing the delivery cylinder 42 mounted
on the delivery drive shaft 54 to also act as a coating applicator
roller, protective coating will be applied to the printed sheet 18
in precise timed registration, and will permit the press to be
operated with its full range of printing stations.
Toward these ends, the coating apparatus 10 of the present
invention includes a relatively simple, positive acting and
economical doctor blade coating unit, generally designated 60,
mounted to the press frame 14 downstream of the delivery drive
shaft 54 and positioned to apply liquid coating material to the
support surface of a delivery cylinder 42 mounted on the delivery
drive shaft. As can best be seen in FIGS. 2, 3 and 4, the doctor
blade coating unit 60 herein comprises a pair of side frames 62,
only one of which is shown, it being understood that the other side
frame is substantially the same as that of the side frame
illustrated, attached to each side of the press frame 14. Pivotally
mounted to one end of each of the side frames 62 is a support
bracket 64 carrying one end of a liquid material reservoir 66 and
cooperating liquid material pickup roller 68 each disposed to
extend laterally across the press 12 parallel with the delivery
drive shaft 54. The coating unit 60 is mounted between the upper
and lower runs of the delivery chains 46 downstream of the delivery
drive shaft 54, and positioned so that the outer peripheral surface
70 of the pickup roller 68 can be engaged with the support surface
of a delivery cylinder 42 mounted on the delivery drive shaft.
As best seen in FIGS. 2 and 3, the support bracket 64 is pivotally
attached to the end of the side frame 62 by a shaft 72 disposed at
the lower end portion of the bracket, and can be pivoted about the
shaft by an extensible cylinder 74, herein shown as a pneumatic
cylinder, one end 76 of which is secured such as by welding to the
side frame, and the opposite end 78 of which is coupled through a
pivot shaft 79 to the upper end portion of the bracket. By
extending or retracting the cylinder 74, the extent of engagement
of the pickup roller 68 against the surface of the applicator
roller 42 can be controlled, and the pickup roller can be
completely disengaged from the applicator roller 42.
The coating pickup roller 68, which is of conventional design and
preferably one such as the Anilox rollers manufactured by A.R.C.
International of Charlotte, N.C. and sold under the name
"PRINTMASTER" having an engraved ceramic or chrome outer peripheral
surface 70, is designed to pick up a predetermined uniform
thickness of liquid coating material or ink from the reservoir 66,
and then uniformly transfer the coating material to the support
surface of the applicator roller 42. To effect rotation of the
pickup roller 68, a suitable motor 80, herein a hydraulic motor, is
attached to one of the side frames 62 and coupled to a suitable
hydraulic fluid source (not shown) through fittings 81A, 81B.
Attached to the output of the motor 80 is an output gear which is
drivingly coupled through a cluster gear 82 and a series of idler
gears 83 each mounted on stub axles 84, to a drive gear 86 attached
to the end of a shaft 88 on which the pickup roller 68 is
concentrically mounted. The shaft 88 of the pickup roller 68 is, in
turn, journaled at each end to the brackets 64 through a releasable
semicircular collar 90 attached by bolts 92 to the bracket. Herein,
the axle of the terminal idler gear, designated 83', also serves as
the shaft 72 for pivotally mounting the support bracket 64 to the
side frame 62 so that when the bracket is rotated about the shaft,
the terminal idler gear remains engaged with the drive gear 86 of
the pickup roller 68.
In this instance, as can best be seen in FIG. 4, the pickup roller
68 has a peripheral surface portion 68P which projects radially
into the reservoir 66 containing the supply of coating material or
ink. A pair of upper and lower inclined doctor blades 94 and 96
attached to the doctor blade head 98 on shoulders 98A, 98B engage
the roller surface to doctor the excess liquid coating material or
ink picked up from the reservoir by the engraved surface 70 of the
roller. The reservoir cavity 66 herein is formed within an
elongated doctor blade head 98 having a generally C-shaped
cross-section with an opening 100 extending longitudinally along
one side facing the pickup roller 68. The reservoir 66 is supplied
with liquid material or ink from a supply drum 102 disposed in a
remote location within or near the press 12. preferably, the doctor
blade head 98 is removably attached to the brackets 64, herein by
bolts 104 having enlarged, knurled heads 106, and which can be
threaded through slots 108 formed in the brackets to clamp the
reservoir in place on the brackets.
To insure that an adequate supply of liquid coating material is
always present within the reservoir 66 and to prevent coagulation
and clogging of the doctor blades 94 and 96 by the liquid coating
material or ink, the coating material or ink is circulated through
the reservoir by two pumps 110 and 112 as shown in FIG. 5. Pump 110
draws the liquid material L from the supply drum 102 via a supply
line 114 and discharges it into a bottom region of the reservoir 66
through a delivery port 114P, and the other pump 112 acts to
provide suction to a pair of return lines 116A, 116B coupled
adjacent a top region of the reservoir through return ports 116P,
116Q for withdrawing excess liquid coating material or ink from the
reservoir. By supplying the coating material or ink from the supply
drum 102 at a greater rate than the rate of withdrawal of material
by the pickup roller 68, a substantially constant supply of coating
material or ink will always be present within the reservoir 66. The
excess coating material or ink which rises above the liquid level
of the return port R (FIG. 8) is suctioned away by the suction
return pump 112.
The general arrangement of the pickup roller 68, doctor blades 94
and 96, and reservoir 66 is similar to that disclosed in U.S. Pat.
No. 4,821,672 entitled "Doctor Blade Assembly With Rotary End Seals
and Interchangeable Heads", the disclosure of which provides
details concerning the end seal structure and operation of a pickup
roller and reservoir usable with the present invention. According
to an important feature of the present invention, however, the
doctor blade reservoir 66 is not pressurized as taught by the prior
art. Instead, coating liquid or ink is supplied to the doctor blade
reservoir 66 by the suction flow produced by the pump 112. In this
arrangement, the suction pump 112 applies a vacuum or suction force
in the reservoir which draws liquid material L from the supply
through the supply conduit 114 to the reservoir and draws excess
liquid material L from the doctor blade reservoir 66 through the
return conduit 116 into the remote reservoir 102 at a rate which is
greater than the rate that liquid coating material or ink is being
supplied to the doctor blade reservoir through the supply conduit
114. Because the suction return flow rate is greater than the
supply flow rate, a positive pressure condition within the doctor
blade reservoir is avoided, and a below atmospheric vacuum pressure
level is provided.
Referring to FIG. 5, FIG. 6, FIG. 7 and FIG. 8, the liquid material
is delivered into the lower region of the doctor blade reservoir
66, and is withdrawn from the doctor blade reservoir near an upper
region of the chamber through the return conduits 116A, 16B. The
liquid level elevation of the return port is preferably selected to
provide for the accumulation of liquid coating material or ink in
more than about half of the doctor blade chamber, thereby insuring
that the engraved surface of the pickup roller 68 will be
thoroughly wetted by the coating material or ink L as it turns
through the doctor blade chamber 66. The reservoir 66 is bounded
vertically by lower and upper doctor head shoulders 98A, 98B.
Accordingly, the return ports 116P, 116Q of return lines 116A, 116B
are located at a liquid level R intermediate the limits established
by the lower and upper shoulders. Any excess liquid coating
material or ink which rises above the liquid level R of the return
ports will be suctioned away by the pump 112.
It will be appreciated that the supply pump 110 is optional, and
that the suction circulation system can be operated effectively
with only the single suction pump 112 as shown in FIG. 6. In the
single pump configuration, it may be necessary to prime the supply
conduit 114 to obtain satisfactory operation. The two pump
arrangement as shown in FIG. 5 is preferred for those installations
in which the supply drum 102 is located at a distance that is too
far from the press to achieve adequate suction flow. The auxiliary
supply pump 110 provides positive flow input to the doctor blade
reservoir at a fixed flow rate. The return suction pump 112 has a
faster suction flow rate than the supply flow rate. Consequently, a
positive pressure buildup in the doctor blade reservoir cannot
occur. By utilizing two pumps as shown in FIG. 5, the liquid level
within the doctor blade chamber 66 can be closely controlled,
without positive pressure buildup, thereby reducing leakage through
the end seals.
Referring to FIG. 8, it will be appreciated that the doctor blade
chamber 66 is maintained at a pressure level below atmospheric by
the suction action of the return flow pump 112. The coating liquid
L rises to the liquid level of the return port R and is drawn off
immediately by the suction pump 112. Additionally, air within the
doctor blade chamber 66 is also evacuated, thereby reducing the
doctor blade chamber pressure to a level below atmospheric. This
negative pressure differential condition opposes leakage of coating
liquid L through the end seals. Since the doctor blade chamber 66
is not positively pressurized, the end seals are operated under
favorable pressure differential conditions, thereby extending their
useful lifetime. Moreover, the negative pressure differential
doctor blade assembly will accommodate a pickup roller having a
chipped corner, which would leak under positive pressure
conditions, but does not leak because of the negative pressure
reservoir condition established by suction flow.
It is useful for the press operator to have an advance warning of
an impending end seal failure. With advance warning, the press
operator can schedule repair and/or replacement of the doctor
blades and the end seals at a convenient time, for example between
press runs or before undertaking the next printing job. Apparatus
for monitoring the suction/vacuum condition within the doctor blade
chamber 66 is provided by a pneumatic sensor circuit 120 as shown
in FIG. 9. The pneumatic sensor circuit 120 includes a pneumatic
sensor line 122 which is coupled in fluid communication with the
doctor blade chamber 66 through a vacuum sensor bore 124 formed
through the upper doctor head shoulder 98B. The vacuum sensor line
122 is coupled to the sensor bore 124 by a threaded fitting
126.
Continuous monitoring of the vacuum/suction condition within the
doctor blade chamber 66 is provided by a vacuum gauge 128 which can
be of any conventional design, for example a Bourdon gauge which is
calibrated for dry air and covers the range from about zero to
about twenty torrs. The vacuum gauge 128 is coupled into the sensor
line 122 by a tee coupling 130. According to this arrangement, the
press operator receives a continuous visual indication of the
vacuum/suction condition within the doctor blade chamber 66.
According to another feature of the invention, the vacuum/suction
line 122 is coupled to a vacuum switch 132. The vacuum switch 132
has a conductive, movable diaphragm 134 which moves into and out of
electrical contact with switch electrodes 132A, 132B. That is, the
diaphragm 134 is pulled out of contacting engagement with the
switch electrodes 132A, 132B when the vacuum/suction level in the
doctor blade chamber 66 is below a predetermined level. When the
pressure level within the doctor blade chamber 66 rises above that
preset level, for example in response to leakage of air through the
end seals or around a worn doctor blade 94, the vacuum force within
the vacuum chamber 132C of the sensor switch also rises, thereby
permitting the conductive switch element 134 to engage the switch
electrodes 132A, 132B.
When switch closure occurs, electrical power is applied to an audio
transducer 136 from a power source 138. Electrical current is
conducted through the pneumatic switch 132 to the audio transducer
136 through power conductors 140, 142. According to this
arrangement, the press operator will receive an audible alert as
soon as the suction/vacuum pressure in the doctor blade chamber
rises above a safe operating level, thereby signaling wear failure
of the doctor blades and/or an impending failure of the end
seals.
From the foregoing, it should be apparent that the coating
apparatus 10 of the present invention provides a highly reliable,
effective and economical in-line apparatus for applying coating
material to the freshly printed sheets 18 in a sheet-fed, offset
rotary printing press 12 which allows the final printing station to
continue to be used as a print station, yet which does not require
any substantial press modification or the addition of a separate
timed applicator roller. While a particular form of the present
invention has been illustrated and described, it should be apparent
that variations and modifications therein can be made without
departing from the spirit and scope of the invention.
* * * * *